1. Field of the Invention
The present invention relates to an ignition coil for an internal combustion engine adapted to supply high voltage to an ignition plug of the engine for generating spark discharge. In particular, the invention relates to an ignition coil, for an internal combustion engine, of a type having a main core portion (also called a main yoke portion) to which a coil is attached, and an auxiliary core portion (also called an auxiliary yoke portion) or a side core portion (also called a side yoke portion), the auxiliary core portion or the side core portion being combined with the main core portion to form a closed magnetic path.
2. Description of the Related Art
The ignition coil for an internal combustion engine as described above is configured as below. A coil is attached to a main core portion (some are provided with an auxiliary core portion), and a side core portion is assembled to the main core portion (an auxiliary core portion and the side core portion are assembled to the main core portion not provided with the auxiliary core portion). The main core portion and the side core portion are set up inside a casing. The coil is connected at its winding-start-end to a terminal of an external-connection connector attached to the casing. In addition, the coil is connected at its winding-terminal-end to a terminal of the plug. Thereafter, an insulating resin is poured into the casing for resin molding.
However, the divided core portions (or including a permanent magnet if the permanent magnet is attached) likely deviate from each other due to external force, molding pressure resulting from the flow of molding resin, or molding strain during hardening, until the resin molding will be finished. Thus, there is a problem in that variations in the performance of ignition coils are increased.
To solve such a problem, an ignition coil disclosed in e.g. JP-2007-194364-A is such that a core holder is installed to hold the positional relationship among three members until the whole will be molded with resin.
JP-8-17657-A discloses an ignition coil as below. A main core portion and an auxiliary core portion are formed integrally with each other. A coil is attached to the main core portion. Thereafter, a side core portion and the auxiliary core portion are engaged and united with each other by press fitting. In addition, JP-8-17657-A describes the fact that the circumferences of core portions are covered by an elastic material to prevent the occurrence of cracking during the molding of mold resin.